Mobile data transmission and data services are constantly making progress, wherein such services provide various communication services, such as voice, video, packet data, messaging, broadcast, etc. In recent years, Long Term Evolution LTE™ has been specified, which uses the Evolved Universal Terrestrial Radio Access Network E-UTRAN as radio communication architecture according to 3GPP specification.
In general, a communication device, such as a so called user equipment UE, may communicate with more than one cell. Communications with more than one cell may be provided so as to increase performance. Such provision may be ensured e.g. based on carrier aggregation CA. In carrier aggregation a plurality of carriers are aggregated to increase bandwidth. Carrier aggregation comprises aggregating a plurality of component carriers.
LTE-Advanced LTE-A is an example of a system capable of providing carrier aggregation. In LTE-A, two or more component carriers CCs can be aggregated in order to support wider transmission bandwidths and/or for spectrum aggregation. Thereby, LTE-Advanced aims to support peak data rates of e.g. 1 Gbps in the downlink and 500 Mbps in the uplink. In order to fulfill such requirements, a transmission bandwidth of up to 100 MHz is required. Since the availability of such large portions of contiguous spectrum is rare in practice, LTE-A utilizes carrier aggregation of multiple CCs to achieve high bandwidth transmission. In doing so, LTE-A supports aggregation of up to five 20 MHz CCs.
Release 10 (i.e. 3GPP TS 36.300) of the E-UTRA specifications introduced Carrier Aggregation CA, where two or more component carriers CCs are aggregated in order to support wider transmission bandwidths up to 100 MHz. In CA it is possible to configure a UE to aggregate a different number of CCs originating from the same eNodeB eNB and of possibly different bandwidths in the uplink UL and downlink DL.
When in CA, a UE is always configured with a primary cell PCell. The PCell is used for security, Non Access Stratum NAS mobility, transmission of a Physical Uplink Control Channel PUCCH (including scheduling requests). All other configured CCs are called secondary cells SCells and do not have PUCCH configured. Furthermore, in CA, the possibility to de-activate CCs/SCells in order to reduce the UE power consumption is supported. The UE monitoring activity of a de-activated SCell is reduced (e.g. no PDCCH monitoring nor Channel Quality Indication CQI measurements are performed) and the UL activity in a de-activated carrier is also stopped (no Sounding Reference Signal SRS).
Moreover, since Release 8 of the 3GPP specifications (i.e. 3GPP TS 36.321), in order to assist the scheduler, the eNB can configure UEs to send Buffer Status Reports BSR and Power Headroom Reports PHR in uplink. BSR indicates the amount of data the UE has available for transmission and are typically used by the eNB to choose an appropriate transport block size while PHR are typically used to select an appropriate modulation and coding scheme MCS and number of allocated Physical Resource Blocks PRBs.
According to the above-mentioned Release 8 specification, among other conditions, in E-UTRA a BSR is triggered in the UE if data arrives in the UE buffer (at Packet Data Convergence Protocol PDCP or Radio Link Control RLC) which has higher priority than the data already available for transmission and/or if new data arrives in an empty UE buffer.
If the UE has no allocation available on the Physical Uplink Shared Channel PUSCH for the Transmission Time Interval TTI where the BSR is triggered, a Scheduling Request SR is then triggered. Once an SR is triggered, a scheduling request is either transmitted on the Physical Uplink Control Channel PUCCH using dedicated resources which are allocated on a UE basis with a certain periodicity by the eNB via RRC signaling, or if no PUCCH is available the scheduling request uses a random access procedure. An SR remains pending until new transmissions are granted to the UE or when a fixed number of scheduling requests on PUCCH have been sent.
Currently, a SR is transmitted in PUCCH, wherein PUCCH is assigned to the PCell. In recent time, it has been discussed to establish a PUCCH also on SCells to reduce the signaling burden of the PCell. Thereby, it was agreed e.g. according to 3GPP Work Item RP-142268 to specify and complete the support of PUCCH on SCell for UEs supporting uplink carrier aggregation.
However, there arises the problem of handling plural PUCCH in carrier aggregation.